Cellular radio systems are currently in increasing use throughout the world, providing telecommunications to mobile users. In order to meet the capacity demand, within the available frequency band allocation, cellular radio systems divide a geographic area to be covered into cells. Each cell is served by a base station through which the mobile stations communicate. The available communication channels are divided between the cells such that the same group of channels are reused by certain cells. The distance between the reused cells is planned such that the co-channel interference is maintained at a tolerable level.
When a new cellular radio system is initially deployed, operators are often interested in maximising the uplink (mobile station to base station) and downlink (base station to mobile station) range. The ranges in many systems are uplink limited due to the relatively low transmitted power levels of hand portable mobile stations. Any increase in range means that fewer cells are required to cover a given geographic area, hence reducing the number of base stations and associated infrastructure costs.
The antenna used at the base station site can potentially make significant improvements to the range and capacity of a cellular radio system. This invention provides a sectored antenna system that combines high Effective Isotropic Radiated Power (EIRP) with high reliability at low cost.
In a known antenna arrangement a single array of antenna elements or several antennas are coupled via beamformers and combiners to a plurality of r.f. transceivers whereby a number of calls are handled simultaneously sharing the same antenna beam. One example of such an arrangement is discussed in a paper presented by S C Swales and M A Beach at the Personal and Mobile Radio Communications Conference, 1991, Warwick. The use of such a system leads to losses within the beamforming and combining means. Further, all the antenna elements/antennas must be capable of handling the combined power of all of the amplifiers which affects both the mean and peak power rating.